1. Field of the Invention
This invention relates to a radio communication system to be used as an automobile telephone system, a portable radio telephone system or a cordless telephone system and more particularly it relates to a radio communication system that enables installation of mobile base devices and portable device.
2. Description of the Related Art
A cellular type automobile telephone system has been known as a mobile radio communication system. Such a system normally comprises a control station, a plurality of base stations and a plurality of mobile stations, of which the control station is connected to a wired telephone network by way of a wire communication path. The base stations are centeredon different radio communication zones. Each of the mobile stations is connected by a radio channel to the base station of a radio communication zone where it is currently located and further to a wire telephone network by way of the base station and the control station.
Such a known system normally employs a so-called frequency division multiple access (FDMA) technique for connection between a base station and each of the mobile stations that belong to it. FDMA is a technique in which a number of radio frequencies are shared by a base station and a plurality of mobile stations. For communication between a base station and a mobile station, the base station picks up an idle radio frequency whenever it calls or is called and then, if the call is successful, the calling and called stations are wirelessly connected by way of the picked up radio frequency. The operation of searching idle frequencies and assigning a particular frequency to a calling or called base station is conducted by the control station.
Now, each of the mobile stations of an automobile telephone system is equipped with an automobile telephone main unit and peripheral equipment including a handset assembly. An automobile telephone main unit comprises radio transmission circuits, control circuits and other circuits. A handset assembly normally comprises a cradle and a handset, which in turn comprises a telephone transmitter, a receiver and a console unit. A console unit in turn comprises dial key, hook switch, an LCD display and other components. The automobile telephone main unit and the handset assembly are connected by a signal cord. The cradle and the handset are connected by a curled cord.
With such an arrangement, the curled cord can constitutes an annoying obstacle when the driver drives and speaks into the telephone transmitter simultaneously. Moreover, the handset cannot be moved away beyond a limit posed by the curled wire, meaning that a passenger sitting on the front or rear passenger seat is compelled to stand up or take a crouching posture if he or she wants to speak over the phone.
While the handset assembly of a conventional mobile station is placed within the passenger cabin of a car, the automobile telephone main unit is normally arranged in the trunk of the car. The signal cord connecting the telephone main unit and the handset assembly should be carefully arranged so as not to aesthetically damage the appearance of the car, entailing a troublesome work to be done within a narrow space of the car.